Posted on March 28, 2013 11:56 am

Ancient Asteroid Caused Global Firestorm

Source:

http://www.sciencedaily.com/releases/2013/03/130327144249.htm

 

New Evidence Ancient Asteroid Caused Global Firestorm On Earth

Mar. 27, 2013 — A new look at conditions after a Manhattan-sized
asteroid slammed into a region of Mexico in the dinosaur days indicates the
event could have triggered a global firestorm that would have burned every twig,
bush and tree on Earth and led to the extinction of 80 percent of all Earth’s
species, says a new University of Colorado Boulder study.

Led by Douglas Robertson of the Cooperative Institute for Research in
Environmental Sciences, or CIRES, the team used models that show the collision
would have vaporized huge amounts of rock that were then blown high above
Earth’s atmosphere. The re-entering ejected material would have heated the upper
atmosphere enough to glow red for several hours at roughly 2,700 degrees
Fahrenheit — about the temperature of an oven broiler element — killing every
living thing not sheltered underground or underwater.

The CU-led team developed an alternate explanation for the fact that there is
little charcoal found at the Cretaceous-Paleogene, or K-Pg, boundary some 66
million years ago when the asteroid struck Earth and the cataclysmic fires are
believed to have occurred. The CU researchers found that similar studies had
corrected their data for changing sedimentation rates. When the charcoal data
were corrected for the same changing sedimentation rates they show an excess of
charcoal, not a deficiency, Robertson said.

"Our data show the conditions back then are consistent with widespread fires
across the planet," said Robertson, a research scientist at CIRES, which is a
joint institute of CU-Boulder and the National Oceanic and Atmospheric
Administration. "Those conditions resulted in 100 percent extinction rates for
about 80 percent of all life on Earth."

A paper on the subject was published online this week in the Journal of
Geophysical Research-Biogeosciences
, a publication of the American
Geophysical Union. Co-authors on the study include CIRES Interim Director
William Lewis, CU Professor Brian Toon of the atmospheric and oceanic sciences
department and the Laboratory for Atmospheric and Space Physics and Peter
Sheehan of the Milwaukee Public Museum in Wisconsin.

Geological evidence indicates the asteroid collided with Earth about 66
million years ago and carved the Chicxulub crater in Mexico’s Yucatan Peninsula
that is more than 110 miles in diameter. In 2010, experts from 33 institutions
worldwide issued a report that concluded the impact at Chicxulub triggered mass
extinctions, including dinosaurs, at the K-Pg boundary.

The conditions leading to the global firestorm were set up by the
vaporization of rock following the impact, which condensed into sand-grain-sized
spheres as they rose above the atmosphere. As the ejected material re-entered
Earth’s atmosphere, it dumped enough heat in the upper atmosphere to trigger an
infrared "heat pulse" so hot it caused the sky to glow red for several hours,
even though part of the radiation was blocked from Earth by the falling
material, he said.

But there was enough infrared radiation from the upper atmosphere that
reached Earth’s surface to create searing conditions that likely ignited tinder,
including dead leaves and pine needles. If a person was on Earth back then, it
would have been like sitting in a broiler oven for two or three hours, said
Robertson.

The amount of energy created by the infrared radiation the day of the
asteroid-Earth collision is mind-boggling, said Robertson. "It’s likely that the
total amount of infrared heat was equal to a 1 megaton bomb exploding every four
miles over the entire Earth."

A 1-megaton hydrogen bomb has about the same explosive power as 80
Hiroshima-type nuclear bombs, he said. The asteroid-Earth collision is thought
to have generated about 100 million megatons of energy, said Robertson.

Some researchers have suggested that a layer of soot found at the K-Pg
boundary layer roughly 66 million years ago was created by the impact itself.
But Robertson and his colleagues calculated that the amount of soot was too high
to have been created during the massive impact event and was consistent with the
amount that would be expected from global fires.

 


Journal Reference:

1.    
Douglas S. Robertson, William M. Lewis, Peter M. Sheehan, Owen B. Toon.
K-Pg extinction: Reevaluation of the heat-fire hypothesis. Journal of
Geophysical Research: Biogeosciences
, 2013; DOI:

10.1002/jgrg.20018